In recent years, multimedia telephone terminals which can be connected to fixed networks have been developed. These terminals provide real-time video, audio, or data, or any combination thereof, between two multimedia telephone terminals over a voice band network connection. Communication may be either one-way or two-way. A multipoint communication using a separate Multipoint Control Unit (MCU) among more than two terminals is also possible. Furthermore, the multimedia telephone terminals can be integrated into PCs or work stations, or can be stand-alone units.
Interworking with such visual telephone systems on mobile radio networks is defined in the ITU-T video/multimedia recommendation H.324/M.
However, in general, a calling party does not know in advance whether or not the terminal of a called party supports the connection type underlying a desired call. Thus, inconvenient error processings and disconnections may occur, if the terminal of the called party does not support the desired connection type, e.g. the multimedia connection.